<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
#div1  {width:200px; height:200px; background-color: aquamarine;}
</style>
<script>
function   toRed()
{ 
    var oDiv=document.getElementById('div1');

oDiv.style.width='300px';
oDiv.style.height='300px';
oDiv.style.background='red';
}

function    toAquamarine()
{
    var oDiv=document.getElementById('div1');

oDiv.style.width='200px';
oDiv.style.height='200px';
oDiv.style.background='aquamarine'
}
</script>
</head>

<body>
<div  id="div1"  onmouseover="toRed()"  onmouseout="toAquamarine()">  
</div>
</body>
</html>